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Abstract

The Ponto-Caspian amphipod Echinogammarus ischnus was first detected at a lone site in the lower Detroit River in 1995, and has quickly spread through the lower Great Lakes. Analysis of archived samples revealed that Echinogammarus was present in the western basin of Lake Erie at Middle Sister, East Sister and Pelee Islands during June 1994. Moreover, body length sizes classes demonstrate that Echinogammarus was a fully reproducing population with different generations at the time of collection in 1994, and that it most likely invaded Lake Erie no later than 1993. It has been suggested that it is displacing the native amphipod Gammarus fasciatus and that replacement of amphipod species could have far-reaching implications. However, no mechanistic studies have been conducted in the laboratory or field to assess habitat preference by invading Echinogammarus or its effects on resident Gammarus populations. Thus, the invasion of Lake Erie by Echinogammarus provides an excellent opportunity to explore interspecific interactions between resident and invading amphipod species. Laboratory and field experiments reveal the interaction between these two species is neutral over short time periods, commensal over brief periods, and negative over longer periods due to abundance patterns of each species. Biomass of Cladophora encrusted on rocks had no effect on Echinogammarus abundance, but it did have positive effects on Gammarus' abundance. Echinogammarus abundance was positively affected by Dreissena -encrusted biomass, while Gammarus abundance fluctuated on Dreissena-encrusted biomass. Thus, introduction and spread of Dreissena in the Great Lakes appears to have facilitated Echinogammarus' colonization, establishment and dispersal in a manner consistent with Simberloff and Von Holle's 'invasional meltdown' hypothesis. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2000 .V355. Source: Masters Abstracts International, Volume: 40-03, page: 0660. Adviser: Hugh J. Macisaac. Thesis (M.Sc.)--University of Windsor (Canada), 2000.